Structural, optical and electronic properties of LaMgHx switchable mirrors

Structural, optical and electronic properties of lanthanum magnesium alloy thin films are studied in situ in real time during hydrogenation. X-ray data show that the as-deposited films contain the intermetallic phase LaMg with CsCl structure as well as fcc β-La and fcc LaHx. Hydrogenation initiates a transformation of β-La to β-LaHx, while the intermetallic phase disproportionates. The fcc structure stays intact during further uptake of hydrogen up to LaH3, and Mg transforms to the rutile structure of MgH2. During hydrogen absorption the alloys change from a good conducting, metallic state with high reflectance, to a transparent color neutral insulator with a band-gap of about 3 eV.